Lever escapement for timepieces



Feb. 14, E NE 2,971,324-

LEVER ESCAPEMENT FOR TIMEPIECES Filed Jan. 28, 1958 IN VEN TOR.

Hndre' Begner BY United States Patent LEVERESCAPEMENTFORTIMEPIECFS AndreBeyner, Neu c'hatel, Switzerland, as'signor to Ebauches S.A., Neuchatel,Switzerland Filed Jan. 28, 1953, SenNo. 711,749 Claims priority,appllcation switzerland Mar. 16,1957

7 Claims. .(Cl.-:58-'-28) The present invention relates "toa leverescapement for timepieces, and more particularly"to a magnetic devicefor holding the lever in its end positions. The-said device isparticularly intended for electric timepieces having a driving bala'ncein which transforma'tion of the reciprocating motion of the balance intoa unidirectional motion is effected by means of an escape mechanismincluding a roller keyed on'thebalance staff, a lever, and an :escape"wheel. The mechanism' being such thatthe escape wheel is controlled bythe lever and is rotated always in the same direction.

Since the escape wheel is driven by the lever, there is no draft effectof the wheel on the lever in order to hold the latter against thebanking pins. The lever, therefore, is free, thus causing a frequentinteraction of the guard pin and of the small roller, which serve forlocking the lever. This interaction impairs the quality of the timingadjustment of the timepiece.

A number of devices have already been proposed for holding the leveragainst the banking pins. Most of these devices are mechanical andinclude springs, jumpers, etc. by means of which the lever can beretained in each of its end positions. These devices are generallydifiicult to construct and must be adjusted by the worker who assemblesthe timepiece and require frequent lubrication.

Another device has been proposed for holding the lever against thebanking pins, chiefly in mechanical watches. In this known device, thearrangement of the escapement is modified so as to do away with thedraft effect of the escape wheel on the lever, and the lever is heldagainst the banking pins by magnetic means, e.g. by magnetic bankingpins. The device forming the subjectmatter of the present invention isbased on this principle but presents many improvements and advantagesover the known construction.

In a timepiece with a driving balance, the motor of which is notpolarized, it is essential that the moving armatures rigidly fixed tothe balance and the stationary armatures or pole shoes of the stator notbecome permanently magnetized as the magnetism would cause a lack ofisochronism. The above-mentioned prior magnetic device leads, owing toits design, to the magnetization of the armatures of the motor throughmagnetic leakage.

The device according to the invention aims at avoiding any magneticleakage. It is broadly characterized by a permanent magnet secured tothe pillar plate of the movement of the timepiece, two magnetic bankingpins bearing against the ends of the said magnet and defining thegeometrical path of the lever and cooperating for this purpose with amember made from a magnetizable material, said member being keyed on thepallet arbor and having two holes in each of which is engaged one ofsaid banking pins, the said member permitting closing practicallycompletely the magnetic circuit of the permanent magnet and providingthe attracting effect required for the lever.

The accompanying-drawing sh'ows,=byway of example, one embodiment-of theinvention.

Fig. 1 is a plan view of this embodiment.

Fig. -2 is a cross se'ction'al view taken along the line II-II in Fig.l. v

Fig. 3 is a fragmentary view of a modification of the invention.

The device illustrated in the drawing comprises a permanent magnet 1consisting of a bar relatively long with respect to its section. Themagnet 1 is made from an'alloy' having'a great remanence and a greatcoercive force, suchas 'the products Ticonal or Alnico (registered tradenames). 'The magnet 1 is magnetized in its longitudinal direction,'so-that, for instance, the south pole is situated 'le'ft-and-thenorthpole right in Figs. 1 and 2. 'Tliepermanent'magnet 1 is secured in amanner not illustrated to the pillar plate 2, in a recess 3 provided inthe'bottom face'ofthe pillar plate 2. Two cylindrical pins 4 and-'5,made from an alloy having a very high magnetic permeability,'-a're"driven into the pillar plate 2 'and' be'ar ag'ain'st the endsofthe'magnet 1. The pins 4 and' S extend at right'a'n'glesto'themagnet 1.The magnet 1, therefore, forms a bridge over the pins 4 and-5.

In order to close as completely as possible the magnetic field of themagnet 1 and of the pins 4 and 5, a magnetic shunt, consisting of ametal sheet 6 cut out from a material having a very high magneticpermeability and a low remanence, is keyed on the pallet arbor 7. Thesection of the shunt 6 is determined in such a manner that it should byno means be saturated by the flux of the permanent magnet 1. In theplate 6 are provided two round holes 8 and 9.

The lever 10, pivoted between the pillar plate 2 and the pallet bridge11, is of the type in which the fork lies by the side of the pallets,but it is to be understood that it might as well be of the type in whichthe fork would lie approximately on the imaginary straight lineconmeeting the axis of the escape wheel to the axis of the lever.

The plate 6 is keyed on the pallet arbor 7 and the pins 4 and 5 arearranged in the pillar plate 2 in such a manner that the movement of thelever 10, defined by its lift angle, is limited by the fact that thewalls of the holes 8 and 9 of the plate 6 come into contact with thebanking pins 4 and 5. Thus, in each of both end positions of the lever10, the magnetic circuit is closed practically without any gap. Itsreluctance is therefore extremely low with respect to the leakagereluctance of the magnet 1 towards the armatures of the motor, whichrepresents a great advantage with respect to the known above-mentioneddevice including merely magnetic banking pins.

On the other hand, the described device has the following advantage:Upon the movement of the lever 10 relatively to the banking pins 4 and5, these pins permanently remain within the round holes 8 and 9 of themagnetic shunt 6, so that the device, during the whole movement of thelever 10, works with very low rcluctances of the magnetic circuit. Sincethe attraction of the shunt 6 by the pins 4 and 5 might be relativelystrong as the shunt 6 sticks to the banking pins 4 and 5, a thin sleeve12 made from a non-magnetic material may be secured to the pins, at theheight of the shunt 6, so as to provide a small gap preventing the shunt6 from sticking to the pins 4 and 5. The sleeve 12 may eonof thepermanent magnet 1, whatever the position of the lever 10 may be.

Although the described device is more particularly intended for use inelectric timepieces with a driving balance, it is to be understood thatit can also be used in mechanical timepieces. v

While I have described and'illustratedone embodiment of my invention, Ido not wish to unnecessarily limit the scope thereQf, but reservethe'right to make such modifications and rearrangements of the severalparts as may come within the purview of the accompanying claims.

What I claim is: g

1. In a timepiece movement, a pillar plate, a spindle, a swingableescapement lever keyed on said spindle, a permanent magnet secured tothe pillar plate, two magnetic banking pins bearing against the ends ofsaid magnet, a member made of a magnetizable material, said member beingkeyed on the spindle of said lever and having two holes in each of whichis engaged with play, one of said banking pins, so as to draw the'leverinto its end positions and to hold it in these positions, said bankingpins thus limiting the oscillatory movement of said lever, said memberbeing so'shaped as to practically completely close the magnetic circuitof the permanent magnet.

2. In a timepiece movement according to claim 1, said permanent magnetconsisting of a bar relatively long with respect to its section andbeing magnetized in its longitudinal direction.

3. In a timepiece movement according to claim 1, a recess provided inthe bottom face of the pillar plate, said permanent magnet beingaccommodated in said recess.

4. ha timepiece movement according to claim 1, said banking pinsextending at right angles to said permanent magnet. V

5. In a timepiece movement according to claim 1, said holes in saidmember being round.

6. In a timepiece movement according to claim 1, said holes in saidmember having an elongated shape.

7. In a timepiece movement according to claim 1, a thin sleeve made of anon-magnetizable material, said sleeve being secured to said bankingpins, at the level of said member, so as to form a small gap preventingsaid member from sticking to said banking pins.

References Cited in the "file of this patent UNITED STATES PATENTS2,669,089 Straumann Feb. 16, 1954 FOREIGN PATENTS 141,629 Australia June18, 1951

